Process for production of glacial acrylic acid by azeotropic distillation with a water entrainer



March 1l, 1969 PROCESS FOR D/S f/L L 427041 Cd. UMIV TcHr-:RKAWSKY FiledMarch 18, 1964 I CONDE/vs 770A/ VESSEL EXCESS /VTPHINEE A/HYROUS3,432,401 PR UCTION 0F GLACIAL ACRYLIC ACID BY AZEOTROPIC DISTILLATIONWITH A WATER ENTRAINER PES/DUE INVENTOR.

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United States Patent O 3,432,401 PROCESS FOR PRODUCTION F GLACIALACRYLIC ACID BY AZEOTROPIC DISTIL- LATION WITH A WATER ENTRAINER ClaudeTcherkawsky, Saint-Avold, Moselle, France,A

assignor to Societe dElectro-Chimie, dElectro- Metallurgie et desAcieries Electriques dUglne, Paris, France, a corporation of FranceFiled Mar. 18, 1964, Ser. No. 352,829 Claims priority, applicationFrance, Mar. 21, 1963,

928,802 Us. cl. 20s- 1s Int. cl. c'lc 51 /46, Bold 3/36, 3/34 5 ClaimsABSTRACT 0F THE DISCLOSURE A process for preparing glacial acrylic acidby treating a solution of from to 80% acrylic acid with an entrainerthat is chemically inert towards the acrylic acid and which is capableof capturing at least 3% water and which has a distillation temperatureat least 5 C. dilerent than that for the acrylic acid. The entrainer andWater form a heteroazeotrope which is `distilled from said acid at atemeprature not over 120 C. and thereafter glacial acrylic acid isobtained by distillation.

This invention relates to a process for production of glacial acrylicacid from dilute aqueous solutions of same by heteroazeotropicentrainment of the water contained in the aqueous solutions.

Processes for the obtention of raw acrylic acid are known, and generallythey comprise treating carbon monoxide with acetylene in the presence ofcatalysts; treating acrylonitrile with aqueous solutions of sulphuricacid; treating ethylene cyanohydrin with aqueous solutions of sulphuricacid; or treating propylene with oxygen in the presence of a catalyst.All these processes give a raw product in the form of an aqueoussolution which generally contains less than 50% by Weight acrylic acid.

Heretofore, obtention of glacial acrylic acid, a product which is atleast 99% acrylic acid, was delicate and dilicult, and all existingprocesses led to insufcient outputs of the glacial acrylic acid. In someof these processes, a

solution of acrylic acid is distilled under a reduced pressure, but animportant portion of the acrylic acid is carried along in an overheadfraction as an aqueous solution. For example, discontinuous distillationof a 500 g. aqueous solution of 50% by weight acrylic acid gives:

A 300 g. aqueous fraction of 16% acrylic acid which must be recycled;

A 190 g. fraction of glacial acrylic acid.

The recovery of glacial acrylic acid is about 76%.

In another process, the acrylic acid is extracted from an aqueoussolution by a solvent or a mixture of solvents with or without metallicsalts. The resulting organic solution is afterwards distilled to obtainglacial acrylic acid. But this process produces no quantitativeextraction of the acid and a substantial quantity of the acid remains inthe water which effects a decreased yield of glacial acrylic acid.

Fractional crystallization does not produce glacial acrylic acid sincean eutectic at 63% by weight of acrylic acid is precipitated.

My invention overcomes the foregoing disadvantages and covers a processfor obtention of glacial acrylic acid from dilute aqueous solutions.Specifically, it comprises quantitatively eliminating the watercontained in the raw acrylic acid Iby heteroazeotropic entrainment byentrainers which form heteroazeotropes with water and do not react withacrylic acid. The process is applicable to any 3,432,401 Patented Mar.11, 1969 which mixture forms a heterogeneous liquid upon condensationthereof. Azeotropic entrainment of the water may be carried out undervarious conditions of pressure, depending on the nature of theentrainer. With some entrainers, it is worked under higher pressure thanatmospheric pressure; however, operating under vacuum or under less thanatmospheric pressure gives better results. I prefer an absolute pressureinferior to 400 mm. Hg. The temperature is limited by polymerization ofacrylic acid, and it is advisable not to heat beyond 120 C. andpreferably to work at temperature below C.

It is preferable that the entrainer have a little solubility in water,form a heteroazeotrope rich in water, be substantially chemically inerttowards said acrylic acid, and be easily separated from acrylic acid bydistillation. An excessive solubility of the entrainer in Water wouldlead to losses of the entrainer through water elimination, and thelatter then has to be redistilled. To make the entrainer efficient, thequantity of water captured by it must be at least 3%, and preferably 7%by weight. Finally, the difference between the distillation temperaturesof the entrainer and of the acrylic acid must be between 5 C. and 100C., and preferably between 15 C. and 40 C.

Examples of the entrainers are: benzene, toluene, esters of acrylic andmethacrylic acids, acrylonitrile, monochlorobenzene, carbontetrachloride, orthodichlorobenzene, etc.

This distillation of the heteroazeotrope may be carried out by acontinuous or a discontinuous process, but it is preferable to operatecontinuously to avoid prolonged super beatings which can alter theproduct. The ulterior separation of the small quantity of entrainerremaining in the glacial acrylic acid is carried out, if desired, byfurther distillation; but this operation is not necessary.

The accompanying. drawing shows one example of continuous industrialinstallation -for practicing my process. Referring to the drawing, adilute aqueous solution of acrylonitrile is introduced through pipe ainto a distillation column I from which the heteroazeotrope exitsthrough conduit b and is condensed in a vessel II and then decanted inapparatus III. The water is eliminated through pipe c and the entraineris returned to the column I through conduit d.

The acrylic acid, practically anhydrous but containing a small amount ofthe entrainer, leaves column I through pipe e and is introduced into acolumn IV where the acrylic acid is separated from excess entrainer. Theseparated entrainer is recycled to column I by conduit f.

The anhydrous acrylic acid exits from column IV through pipe g and isintroduced into a column V where the pure acrylic acid is removedthrough pipe h and residues are obtained through line i.

The following, non-limitative examples illustrate may process. Thementioned percentages must be understood in percent by weight.

EXAMPLE I 500 g. of an aqueous Solution of a 50% acrylic acid and g. ofbenzene as an entrainer were introduced into a one-liter llasksurmounted by a Fenske ring-column to which is connected a condenser.`0.5 g. of hydroquinone and 1 g. of copper turnings as polymerizationinhibitors were added to the ask.

Distillation was effected under an absolute pressure of 200 mm. Hg and abenzene-water heteroazeotrope passed at 37 C. The benzene was sent backinto the flask as a reflux, and 249 g. of water containing 0.1% acrylicacid were recovered. After substantially complete elimination of thewater, distillation temperature rose and 103 g. of a benzene solutioncontaining 4% acrylic acid were recovered. This acrylic acid was notlost as the benzene solution was reutilized in further operations.

Then the vacuum was extended to an absolute pressure of 100 mm. Hg at atemperature of 87 C., and the distillation was completed. 240 g. of99.8% glacial acrylic acid (percentage determined by measuring acidity)and containing less than 0.01% benzene (determined by vaporchromatography) were obtained.

The amount of acrylic acid obtained as glacial acid was 95.8% of thetotal amount of acrylic acid utilized.

EXAMPLE II The operation was carried out in the same apparatus ashereabove, but the benzene was replaced by toluene.

The entire distillation was effected under a pressure of 100 mrn. Hg atincreasing temperatures and at 38 C. a water-toluene heteroazeotrope wasobtained. After separation of this heteroazeotrope into two phases, thetoluene was sent back as reux into the ask. When formation of theheteroazeotrope stopped, the temperature rose to 53 C. and a dilutesolution of acrylic acid in toluene was obtained. After elimination ofthe toluene, the ternperature rose to 87 C. and then the glacial acrylicacid desired was recovered.

The three fractions obtained were respectively formed of:

249 g. water containing 0.1% acrylic acid, 109 g. toluene containing 9%acrylic acid, 236 g. of 99.7% glacial acrylic acid which contained lessthan 0.03% toluene.

The amount of acrylic acid obtained as glacial acrylic acid reached 94%of the total amount utilized.

EXAMPLE III Into a semi-industrial installation for discontinuousdistillation were charged 2000 kg. of a mixture containing:

Percent Acrylic acid 45 Water 45 Entrainer, acrylonitrile 2 kg. ofhydroquinone and 5 kg. of copper turnings as polymerization inhibitorswere added.

Distillation was effected under an absolute pressure of 200 mm. Hg andan acrylonitrile-water heteroazeotrope passed at 35 C. Aftercondensation and decanting, two phases were obtained: one, composedessentially of acrylonitrile, was sent back as reflux into thedistillation column; and, the other, aqueous, was drawn off.

960 kg. of the recovered aqueous solution contained 7.3% acrylonitrileand 0.08% acrylic acid. This solution can be distilled again to recoverthe acrylonitrile contained therein, or can be used to produce acrylicacid by hydrolysis of the acrylonitrile.

When there was no water left, the temperature rose to 40.5 C., and then132 kg. of acrylonitrile containing 4% acrylic acid were recovered.

Then the vacuum was extended to an absolute pressure 4 of mm. Hg and 885kg. of 99.8% glacial acrylic acid containing 0.02% acrylonitrile wereobtained.

The amount of acrylic acid obtained as glacial acid was 98% of the totalamount utilized.

While I have shown and described preferred embodiments of my invention,it may be otherwise embodied within the scope of the appended claims.

I claim:

1. A process for the production of at least 98% glacial acrylic acidfrom an aqueous solution containing 10% to 80% acrylic acid comprising:

(A) adding to said solution an entrainer that is chemically inerttowards the acrylic acid to form a heteroazeotrope of the entrainer andwater that has a distillation temperature at least 5 C. different fromthe distillation temperature of acrylic acid; and,

(B) heating said acrylic acid and heteroazeotrope to a temperature notgreater than C. to separate by distillation the heteroazeotrope fromsaid acid.

2. The -process of claim 1 characterized by said entrainer beingselected from the group consisting of benzene, toluene, esters ofacrylic and methacrylic acids, acrylonitrile, monochlorobenzene, carbontetrachloride and orthodichlorobenzene.

3. The process of claim 1 characterized by carrying out saiddistillation of said heteroazeotrope under an absolute pressure lessthan substantially about 400 m-m. Hg.

4. A process for the production of at least 98% glacial acrylic acidfrom an aqueous solution containing 10% to 80% acrylic acid comprising:

(A) adding to said solution an entrainer that is chemically inerttowards said acrylic acid to form a heteroazeotrope of the entrainer andwater that has a distillation temperature at least 5 C. different fromthe distillation temperature of acrylic acid;

(B) heating said acrylic acid and heteroazeotrope to a temperature notgreater than 120 C. to separate by distillation the heteroazeotrope fromsaid acid; and,

(C) continuing said heating to substantially eliminate any remainingentrainer from said acid to form at least 98% glacial acrylic acid.

5. The process of claim 4 characterized by said entrainer being selectedfrom the group consisting of benzene, toluene, esters of acrylic andmethacrylic acids, acrylonitrile, monochlorobenzene, carbontetrachloride and orthodichlorobenzene.

References Cited UNITED STATES PATENTS 1,668,380 5/1928 Ricard 203-151,915,002 6/1933 Ricard et al 203--15 2,033,978 3/1936 Dreyfus 203-163,337,740 8/1967 Gray et al 203-69 FOREIGN PATENTS 1,169,740 9/ 1958France.

OTHER REFERENCES Weissberger, Distillation, Technique of OrganicChemistry, vol. IV, 1st edition, New York, Interscience, 1951, p. 363.

WILBUR L. BASCOMB, Primary Examiner.

U.S. Cl. X.R.

